1. Field of the invention
The invention concerns a bridge for connecting an IEEE 802.3 local area network to an asynchronous time-division multiplex telecommunication network. This type of local area network is characterized by a carrier detection and collision detection access method. It is marketed under the tradename ETHERNET, among others.
2. Description of the prior art
It is often desirable to transmit data from one local area network to another via a telecommunication network. When this is a conventional synchronous time-division multiplex telecommunication network, a known technique is to connect each local area network to the telecommunication network by means of a leased line having a bit rate of 2 Mbit/s for each direction using a device called a bridge. A known type bridge transmits in full the content of frames carried by the local area network bus, including the header and synchronization bits which are of no relevance to the link to another local area network. The drawback of synchronous time-division multiplex telecommunication networks for linking local area networks is that the bit rate is limited to 2 Mbit/s.
It is known that future asynchronous time-division multiplex telecommunication networks will enable data to be transmitted at much higher bit rates, up to 600 Mbit/s. The journal Revue des Telecommunications, volume 62, No 3/4/1988 describes a protocol for data transmission in an asynchronous time-division multiplex telecommunication network between stations internal or external to the network. French patent application No 89 04168 describes a signalling message processor implementing this protocol.
The functions of layer 2.1 of an asynchronous time-division multiplex telecommunication network data transmission protocol are:
to detect transmission errors by means of cyclic redundancy check bits;
to detect lost cells by means of numbering bits placed in a field of each cell provided for check bits;
to segment the data of a message before transmitting it in the form of cells each containing 28 data bytes;
to reassemble the data of each message after the cells containing them are received.
An object of the present invention is to propose a bridge for connecting each IEEE 802.3 local area network to an asynchronous time-division multiplex telecommunication network using a known protocol for data transmission in an asynchronous time-division multiplex telecommunication network, in particular the protocol described in the abovementioned documents, to provide a high bit rate link between widely separated local area networks.